Mercury tube switch



April 25, 1933. D w DAv|$ 1,905,813

MERCURY TUBE SWITCH Filed Dec. 24, 1932 Inventor, Dean W Davis,

y mmwm Attorneys.

Patented Apr. 25, 13

UNITED STATES -PATENT OFFICE DEAN W. DAVIS, OF PENDLEION,' INDIANA, ASSIGNOR TO JOSEPH H. STALEY, OF

' COLUMBUS, INDIANA MERCURY TUBE SWITCH V This invention relates to electric current flow control switches and particularly to that type of a switch in which a circuit is closed or opened by means of a shiftable element moved 5 by either rocking the element or subjecting 1t to a change in motion to utilize its inertia effect. This invention is a continuation in part of the invention described and claimed in my copending application for U. S. Letters Patent filed November 19, 1931, Serial No.

One of the important objects of my invention is to provide a very simple and extremely durable structure which may be-produced at a relatively low cost.

Another important object of the invention is to provide a structure in which glass or other like material may be eliminated as a container for mercury and the mercury employed in direct contact with a metallic container.

A further important object of the invention is to provide means for effecting a permanent, non-deteriorating seal and connection between two parts of the mercury container.

These and other objects and advantages will become apparent 'to those skilled in the art in the following description of the invention as illustrated by the accompanying drawing in which Fig. 1 is a fragmentary side elevation of one particular form of my invention as applied to a rocking type switch with the switch in the closed position, and

5 I Fig. 2, a fragmentary side elevation of the same structure rocked to the open position.

Like characters of reference indicate like parts in the two views in the drawing.

Heretofore it has been customary to place 40 a quantity of mercury within a glass tube, seal at least two electrodes through the glass, and to evacuate the tube. By mounting the glass tube in a suitable holder, the tube could be rocked whereby the mercury could be made 4 to flow to interconnect the two ends of the electrodes extending to within the tube. Switches of this type are not only expensive to make but are extremely fragile and not suitable for use in rough work or where sudden jolts or vibrations are encountered.

Referring to the drawing, I form a metal tube 10 closed at one end and open at the other, and within it I place a quantity of mercury 11. I form a bushing 12 of some insulating material such as cellulose fiber, rubber, asbestos and the like. The essential characteristics of the insulating material to be employed are that it be compressible and resilient; have no contaminating effect on mercury; be non-conducting as to electricity; and be non-deteriorating throughout the life of the switch. This bushing 12 is formed to have an internal diameter to permit it to be slipped, over the outer side of the open end of the tubelO and it is formed with a shoulder- 13 therein to seat against the end of the tube 10. The shoulder 13 is formed by providing a hole through the bushing 12 beyond the end of the tube 10 to have a smaller diameter than that of the inner wall of the tube 10.

A metallic cap 14 is formed to haveja closed end and an internal diameter slightly less than the external diameter of the bushing 12 and is forced by its open end over the bushing to have the cap 14, by its side wall, press the bushing tightly against and around the tube 10. The bushing thus forms a seal with the cap as well as with the tube by being compressed between the two members. The cap 14 is formed to havea pocket or chamber 15 beyond the outer end of the bushing 12.. The chamber is formed to have a shoulder therearound to strike the end of the bushin g'and limit the travel of the cap thereover.

The metal selected from which the tube 10 and cap 14 are made must be of such a nature that it will not combine or amalgamate with the mercury. I find iron or steel to be entirely suitable. While the original air content within the tube 10 and the .cap 14 is small and the oxidizing effect is negligible after the cap 14 is positioned over the bushing 12 as above indicated, if considered necessary, all of the oxygen within the tube 10 after the mercury is placed therein may be driven out by placing a small piece of dry ice or solidified carbon dioxide therein and allowing it to melt so as to have the gaseous carbon dioxide push out the air and permit the cap 14 to be placed over the tube 10 to 100 the tube toward the shoulder 13 of the bushing 12 and build up slightly higher than the lower edge of the opening through the bush ing before the mercury will flow on through. that opening with a rush into the pocket 15 of the cap 14 beyond the bushing. The quantity of mercury employed is suflicient to fill this pocket 15 and extend through the bore in the bushing 12 back into the tube 10 so that the mercury is then in contact with both the tube 10 and the cap 14 with a portion thereof being within the bore within the bushing 12 and interconnecting the mercury on either side thereof.

Referring to Fig. 2, when the tube 10 is rocked in the opposite direction, the mercury will tend to flow to the closed end of the tube 10. However a small mass of the mercury will be left within the pocket 15 in the cap 14 and the level of the remainder of the mercury will be then below the lower edge of the bore through the bushing 12 whereby the mercury is then no longer in contact continuously with both the cap 14 and the tube 10. By reason of the combined eflect of the surface tension of the mercury and the sharp shoulder at the end of the bore through the bushing 12, the mercury will drop down and away from the inneredge .oi the shoulder sharply soas to effect a quick severance of the mercury between the cap 14 and the'tube 10.

In practice the tube 10 and its cap 14 when assembled as above indicated, form a unitary cartridge-like structure which is mounted between clips 16 and 17 extending from any suitable base 18. Electrical conductors 19 and 20 lead from the respective clips 16 and 17. Thus it is to be seen that by rocking the base 18, Figs. 1 and 2, the gap between the conductors 19 and 20 may be closed and opened by the flow of mercury to first form an electrical path between the tube 10 and the cap 14 over the intermediate insulating bushing 12 and the circuit opened by rocking. the base 18 in the opposite direction to cause the mercury to flow away from the cap 14. Both the tube 10 and the cap 14 being made I of metal, there is no danger of accidental breakage and the combined structure may be readily inserted in a circuit between clips without having to solder connections. More over the mercury is in contact with a; considerable area of metal as opposed to the heretofore commonly employed wire electrodes. While I have here shown and described my invention in the best form as now known to me, it is obvious that structural deviations may be employed without departing from the spirit of the invention and I do not desire to be limited to that precise form beyond the limitations as may be required'by the following claims.

1'. claim:

1. In a mercury switch, the combination of a metallic tube closed at one end, a metallic cap having a chamber and overlapping the open end of the tube, a compressible, resilient, insulating bushing interposed between and having sealing contact with the tube and cap, said bushing having a projection extending above the bottom of the'tube to provide a dam therebetween and the chamber, and a mass of mercury bridgeable across the projection to electrically connect the tube and cap.

2. In a mercury switch, the combination of a metallic tube closed at one end, a bushing of compressible, resilient, insulating material exteriorly engaging the open end of the tube and having an internal shoulder abutting against the end edge of the tube, a metallic cap compressibly engaging the exterior of the bushing and having a chamber communicating with the opening through the bushing, said tube and cap being positioned by said shoulder, a mass of mercury normally located in said chamber, and a sewnd mass of mercury in said tube adapted to bridge said shoulder to merge with the mercury in said chamber and electrically connect said tube and cap. 7

3. In a mercury switch, the combination of a metallic tube closed at one end, a bushing of compressible, resilient, insulating material exteriorly engaging the open end of the tube and having an internal shoulder abutting" against the end edge of the tube, a metallic cap having a socket for receiving and compressibly engaging the exterior of the bushing to sealably connect the same with the tube and cap, said tube and cap being positioned by said shoulder, the bottom of the socket being tapered to limit the insertion'of the bushing in the cap, and a mass of ing of compressible, resilient, insulating ma terial exteriorly engaging the open end of the tube and having an internal shoulder abutting against the end edge of the tube, a-

metallic cap compressibly engaging the exterior of the bushing and'having a chamber communicating with the opening through the bushing, a mass of mercury normally'lo- Lemma dated in said chamber, and a, second mass of mercury in said tube ada ted to brid e said shoulder to merge with t e mercury msaid chamber and electrically connect said tube and cap.

In testimony whereof I afix my signature.

DEAN W. DAVIS. 

